This application incorporates by reference Taiwanese application Serial No. 90114780, Filed Jun. 18, 2001.
1. Field of the Invention
This invention relates to a long seek control system and method, and more particularly, to a long seek control system and method in an optical storage device.
2. Description of Related Art
As the need of storage medium with high capacity greatly increases, optical storage devices now play an essential role. It has been a critical issue to reduce the data access time when reading data from the optical disc.
In a conventional optical drive, a disc is disposed on a spindle motor, which rotates the disc. The disc has multiple tracks for storing digital information, which is read by an optical pickup head. The optical pickup head is disposed on a sled. A sled driving motor can drive the sled, whereby the pickup head can reach the desired position for reading information of the disc.
The reading process of an optical drive includes the following steps. First, after turning on the optical drive, the optical disc is rotated by the spindle motor. Then, the optical pickup head is moved to the inner ring of the optical disc. After that, a focus servo of the optical drive is activated to emit a laser beam and focus the laser beam to form a laser spot on the optical disc. Then, a tracking servo of the optical drive is activated to move a lens of the optical pickup head and let the laser spot follow a single information track. After that, a track number is read out to know the present location of the optical pickup head. Next, a long seek operation is performed, that is, the seek servo of the optical drive is activated to move the optical pickup head from the present track to the vicinity of the target track. Then, the tracking operation is performed and the optical pickup head reads its present track number for knowing the difference from the target track number. Then, a short seek operation is performed, that is, the lens is moved with fine adjustment on its location to move the laser spot to the target track. Then, tracking operation is activated and the data of the optical disc is read out.
In the foregoing descriptions, the long seek operation of the optical drive is the main factor that affects the averaged seek time. During the long seek operation, the optical pickup head must fast accelerate or decelerate to reduce the seek time. Furthermore, during the moving operation of the optical pickup head, the vibration of the optical pickup head should be avoided to reduce the focus loss. Even more, during the long seek operation, the problem of track count missing should be also avoided to reduce the error between the track number of the optical pickup head and the target track number. All the above factors are necessary to be considered when the long seek system is designed.
FIG. 1 schematically illustrates the dual actuator system used in a long seek operation. In FIG. 1, the dual actuator system used in the long seek operation is composed of a sled actuator 102 and a fine actuator 104. A lens 106 of the optical pickup head (not shown) is mounted on the fine actuator 104. During the seeking operation, the sled actuator 102 moves the fine actuator 104 back and forth on the actuator track 108, so as to let the lens 106 remain at the central of moving range of the fine actuator 104. A proper control on the sled actuator 102 and the fine actuator 104 is necessary to assure that the laser spot can be precisely projected onto the optical disc 114, which is affixed on the damper 110 and driven by the spindle motor 112. The sled actuator 102 usually is a sled motor, and the fine actuator 104 usually is a voice coil motor (VCM). The lens 106 is coupled to the sled through a spring coil of the VCM.
FIG. 2 schematically illustrates a conventional long seek control system. In FIG. 2, after the target track (JT) is inputted to the system, a subtraction between the target track and the actual track (AT) is done, and a residual track count (RTC) is obtained. The RTC is inputted to reference velocity mapping unit 202 and output a reference velocity Vref, which serves as a reference for the optical pickup head during reading information. The reference velocity Vref is inputted to a sled actuator 208. The fine actuator 210 is used to adjust the location of the lens. The sled actuator 208 is used to move the sled (not shown in FIG. 2). The actual track AT is generated by a track count sensor 212 according to the displacement y of the dual actuator. The track count sensor 212, for example, uses the signals of radio frequency zero crossing (RFZC) or tracking error zero crossing (TEZC) generated by the optical pickup head to obtain the actual track AT.
The reference velocity curve used by the reference velocity mapping unit 202 in the conventional long seek control system is shown in FIG. 3. The horizontal axis of FIG. 3 is the residual track count RTC and the vertical axis of FIG. 3 is the reference velocity Vref of the dual actuator. When the RTC is less than r0, the mapping relation between the RTC and the reference velocity Vref is linear. When the RTC is greater than r0, the mapping relation between the RTC and the reference velocity Vref is a quadratic function.
FIG. 4 is a curve of velocity versus time for the dual actuator in a conventional optical drive. The horizontal axis of FIG. 4 represents the time, and the vertical axis of FIG. 4 represents the reference velocity of the dual actuator. When the time is at t0, the dual actuator starts to decelerate, and when the time is at t1, the dual actuator stops. Since the velocity variation of the dual actuator is very large, it causes the dual actuator unstable. In other words, when the optical pickup head moves close to the target track, the vibration occurs and causes focus loss. The research of reducing the focus loss and track count miss is still strongly needed.
It is an objective of the present invention to provide a long seek control system and method for an optical drive. The invention reduces the long seek time and avoids the vibration of the optical pickup head. Thus, the invention makes the optical drive more stable.
In accordance with the foregoing objective and other objectives of the present invention, the invention provides a long seek control system and method for receiving a target track and controlling a dual actuator of the optical drive. The location of the dual actuator is corresponding to the displacement of the dual actuator. The dual actuator is composed of a sled actuator and a fine actuator. The long seek control system includes a reference velocity mapping unit, a velocity estimator, and an electrical damper. The reference velocity mapping unit is used to receive the target track and a residual track count after subtraction by the actual track, and obtains a reference velocity for the dual actuator. The velocity estimator is used to receive the actual track, and output an estimated velocity. The result of the reference velocity being subtracted by the estimated velocity is corresponding to a sled control effort. The electrical damper is used to receive the sled control effort, and simultaneously receive the displacement of the dual actuator, so as to output a damping control effort to the fine actuator and reduce the vibration of the fine actuator during the long seek operation. In the reference velocity mapping unit, a reference velocity curve is used to describe the mapping relation between the residual track count and the reference velocity. The reference velocity curve includes a linear part and several quadratic parts with different quadratic functions.